The present invention relates to a damping compressor and to a method for generating compressed air via damping.
The tires of commercial vehicles are usually supplied with compressed air. Nowadays, the energy which is required to generate compressed air is usually applied by the drive motor by way of a compressor. In commercial vehicles, this compressor should therefore supply sufficient compressed air to supply the tires both of the traction vehicle (tractor) and of the trailer. In this context, it is significant that commercial vehicle tires are often operated with air pressures above 9 bar.
The problem with the systems mainly used today is that, on the one hand, the energy which has to be applied by the drive motor to operate the compressor greatly reduces the achievable overall efficiency level, i.e. the efficiency level is only a few percent and, on the other hand, with these systems the trailer can only be supplied with compressed air up to 9 bar by the traction vehicle. In order to ensure the correct tire pressure also in the trailer, automatic tire pressure control systems are being increasingly used. However, these systems require additional expenditure to increase the pressure.
At the same time, when a commercial vehicle is operated, the chassis of the vehicle should be damped in order to ensure reliable driving dynamics. The method of functioning of currently used systems can be considered to be equivalent to the conversion of motion energy into heat.
An approach which is known in the prior art uses a pneumatic booster to increase the pressure for a tire pressure control system. However, the use of such a booster or air quantity/air pressure booster degrades the efficiency level of such a system further.
There is therefore needed an improved device for generating compressed air in a vehicle.
The present invention is based on the idea that vibrations of the vehicle lead to a relative stroke motion between the chassis and axle which is transmitted to two elements of a damper (for example, a shock absorber) of the vehicle. This relative stroke motion between the two elements can be used to change an air volume between the elements and therefore generate compressed air as a damping compressor. In particular, with the proposed approach it is possible for the zero crossing of the elements during the spring compression and spring extension to define a central position or position of rest in which an air volume between the elements is at a minimum or is not present. As a result, a dead space between the elements is minimized and, as a result, a pumping effect is achieved with approximately each spring compression stroke and/or spring extension stroke, allowing the efficiency level of such a compressor to be maximized.
It is advantageously possible for the use of the energy which is released during damping to generate compressed air, therefore providing savings in terms of the fuel which would be required to operate a compressor in order to generate compressed air by means of the drive motor. Given such a combination of a damper and a compressor, the use of a separate (for example hydraulic) damper and of a separate compressor also becomes unnecessary, as a result of which the manufacturing costs when using the proposed approach can be reduced. A further advantage is achieved by virtue of the fact that the damper is not so strongly heated because the majority of the damping energy is not converted into heat but rather stored as compressed air. Since the system which is proposed here can be used, in particular, also in the trailer of a commercial vehicle, a widely selectable pressure level can be set in components of the trailer independently of the traction vehicle. Even a complete or at least partial compressed air supply of the traction vehicle by components of the trailer is possible. This means that under certain circumstances it is possible to completely dispense with the compressor in the traction vehicle (or it can be at least simplified and/or made smaller).
In this way, the damping compressor can be advantageously used as a redundant safety system for the traction vehicle compressor and therefore for increasing the failsafety of the traction compressor.
Since the air which is to be used for the generation of compressed air is preferably obtained from a buffer which can be connected to the damping compressor, changing the air pressure in such a buffer also allows variable damping by virtue of pressure levels which can be set to different values. Since this system for generating compressed air mainly makes use of the components which are used in any case in a shock absorber, and hardly any additional elements are required, the design and structure of the approach which is proposed here can be kept simple. Using the energy which has been produced by the damping of a vehicle to generate compressed air is therefore both economically and ecologically very sensible.
The present invention therefore provides a damping compressor which is designed to generate compressed air by damping a relative motion between an axle and a chassis of a vehicle.
According to one specific embodiment of the invention, the damping compressor has the following features:
(a) a compressor arrangement which comprises a first element and a second element, wherein the first element can be connected to the axle or to the chassis of the vehicle, and the second element can be connected to the other of the chassis or the axle of the vehicle, wherein the arrangement is designed, to change an air volume between the first element and the second element in order to generate the compressed air in the case of a relative stroke motion between these elements, wherein the compressor arrangement also has a minimum of the air volume or no air volume between the first and second elements in a position of rest;
(b) a driver element which is designed to bring about an increase in air volume in the case of a relative motion between the axle and the chassis by entraining the first element in a stroke direction; and
(c) a restoring element which is designed to move the first element counter to the stroke direction, as a result of which a reduction in the air volume is brought about and the compressed air is expelled from the compressor arrangement.
Such an embodiment of the invention provides the advantage that by virtue of the use of two elements which can be moved relative to one another, a position of rest in which an air volume between the elements tends toward zero can be achieved for both elements. As a result, a maximum efficiency level of the approach according to the invention can be achieved. The two elements which are used can be two movable pistons which act as a pressure-generating piston and as a corresponding piston. Alternatively, a container wall or a container floor can also be used as first and second elements of the damping arrangement in the context of a movable piston. The restoring element easily permits the first element to reliably reach the position of rest again.
According to a further embodiment of the invention, the driver element can be designed to bring about an increase in the air volume in the case of a further relative motion between the axle and the chassis by entrainment of the second element in a direction which is opposed to the stroke direction, wherein the damping compressor has a further restoring element which is designed to move the second element in the stroke direction, as a result of which a reduction in the air volume is brought about and the compressed air is expelled from the compressor arrangement. Such an embodiment of the invention provides the advantage of continuous use of the proposed principle of the generation of compressed air since the stroke of the one element is directly followed by the stroke of the second element which immediately initiates a gain in compressed air again. As a result, a motion of the driver element which is opposed to the stroke direction beyond the position of rest of one of the elements, i.e. a motion in the stroke direction and a motion in the direction counter to the stroke direction, can also be utilized to generate compressed air. This leads to a significant extension of the possibility for generating compressed air and therefore to an improvement in the efficiency level of the damper compressor.
According to a further embodiment of the invention, the driver element can be embodied in a rod shape with a thickened portion, wherein the thickened portion can be arranged on the rod-shaped element in such a way that the thickened portion is arranged between the first element and the second element. This advantageously permits the two elements to move in opposite directions with merely one driver element, which, by virtue of the rod-shaped embodiment, is also particularly flexurally strong with respect to the traction forces and compression forces which occur.
According to a further embodiment of the invention, the driver element is led through at least the first element and/or the second element. The first and/or second element are therefore guided along the motion axis of the damping compressor according to the invention, as a result of which a relative motion between the chassis and the axle results in the largest possible stroke motion of the first element with respect to the second element.
According to a further embodiment, the restoring element and/or the further restoring element can be a spring. This provides the advantage that elements which involve already mature technology, are widely available, and are cost-effectively available, can be used.
According to a further embodiment of the invention, the damping compressor has an inlet valve which is designed to let air from external surroundings of the damping compressor and/or from an air container, in particular a spring bellows, into the air volume between the first element and the second element, during the relative stroke motion. The extraction of the air from the air container has the advantage that air which has already been cleaned and dried is available and can be re-used easily and efficiently. Extraction of the air from the external surroundings of the damping compressor has the advantage that it is possible to make available, for example for tires, a compressed air supply which is independent of the air supply of the traction vehicle, or even to assume the function of supplying compressed air to the traction vehicle.
When the invention is configured in the form that the air which is used for changing the air volume between the two elements is sucked in directly from the atmosphere, said air is preferably cleaned before use since it may contain dirt and water. Dirt can be removed by means of a suitable air filter upstream of the damping compressor in the direction of flow. There are various ways of drying the air, wherein the first way may be that it can firstly be compressed to a significantly higher pressure than that required by the load system and can be stored in a buffer. It cools down here, as a result of which the water contained therein condenses and can be discharged via a manually or automatically acting discharge valve. Starting from the buffer, the air can be relaxed by means of a pressure control valve to the pressure required by the load system and can be fed to the load system. The reduction in pressure causes the relative humidity of the air to drop. This procedure also makes it possible to influence the damping effect by varying the pressure in the buffer. Although this procedure has a relatively low efficiency level, there is generally much more damping energy available in any case than is required for the air supply for generating compressed air. According to another embodiment, a conventional air dryer, which is regenerated from time to time, may be connected downstream. A continuously acting diaphragm dryer may be connected downstream as a further alternative.
The air which is to be used for the change in volume between the elements can preferably be sucked in from a reservoir which is supplied by the traction vehicle. The air should then only be subsequently compressed to the relatively high supply pressure or for the tire pressure control system. Since the air has already been conditioned by the traction vehicle, it is then no longer necessary to perform drying or cleaning.
According to another embodiment, the air can also be sucked in from a low pressure reservoir which collects, in a closed system, the air which has been discharged by other systems, for example the air suspension system, brake system or tire, which air was originally supplied by the traction vehicle. The air is also already conditioned by the traction vehicle here. It is no longer necessary to perform drying or cleaning.
Of course, a combination of the various ways of sucking in air, some of which are mentioned above, may also be done, with the result that, on the one hand, air can be sucked in from the atmosphere but, on the other hand, air can also be made available by a reservoir which is supplied by the traction vehicle, or air can be made available from a low pressure reservoir.
According to a further embodiment of the invention, the damping compressor has an outlet valve in the first element and/or second element, which outlet valve is designed to eject the compressed air into a compressed air accumulator. In particular, the outlet valve can be embodied as a nonreturn valve such as, for example, a reed valve. This provides the advantage that the air volume between the first and second elements can be kept as small as possible, since the compressed air which is generated can escape from the air volume while the pressure generated is maintained by the first and/or second element.
According to a further embodiment of the invention, the compressed air accumulator is designed to make available compressed air in order to move the first element counter to the stroke direction and/or to move the second element in the stroke direction, as a result of which a reduction in air volume is brought about and the compressed air is generated. In this way, the compressed air in the compressed air accumulator can advantageously be used to attenuate the relative motion of the axle with respect to the chassis.
According to a further embodiment of the invention, the first element and the second element are each formed by a piston. It is to be considered advantageous here that two virtually identical components can be used to generate compressed air. Furthermore, such a configuration permits technically a very simple generation of compressed air both during spring compression and spring extension.
According to a further embodiment of the invention, the damping compressor has a guide element which is designed to receive and to guide the first element and the second element during a relative motion between the axle and the chassis, wherein the guide element has at least one shoulder on an inner wall, on which shoulder the first element and the second element bear in the position of rest. The guide element can be, for example, a cylinder in which the first and/or second elements move. Such an embodiment of the invention can assist guidance of the first and/or second elements along the motion axis of the damping compressor. The use of such a shoulder which is technically easy to manufacture provides the advantage that its use allows the position of rest to be easily defined and permits a volume which tends towards zero between the first and second elements to be achieved in the position of rest in combination with the restoring elements.
According to one alternative embodiment of the invention, the first element and the second element are each formed via a cylinder, wherein the cylinders are arranged one in the other and the bottom of the cylinder which is arranged on the inside acts as a piston. Such an arrangement provides the advantage of ease of maintenance during which, if appropriate, the cylinders can easily be replaced.
According to one alternative embodiment of the invention, the damping compressor has a guide element which is designed to receive and to guide the first element and the second element during a relative motion between the axle and the chassis, wherein the cylinder which is arranged on the inside has a holding unit which is designed to fit onto an outer surface of the guide element in order to define the position of rest of the cylinder which is arranged on the inside, and wherein the cylinder which is arranged on the outside has a cylinder wall which is designed to fit on an inner wall of the guide element in order to define the position of rest of the cylinder which is arranged on the outside. Such an embodiment has the advantage that the position of rest can be defined precisely both for the inner and for the outer cylinders in a simple manner.
According to a further embodiment of the invention, a length of the driver element can be adjusted, in particular by use of an electric spindle drive and/or a hydraulic intermediate element. A position of rest for the first and/or second elements can advantageously therefore be set even if no air suspension system or another suspension system of the commercial vehicle which allows the position of rest to be permanently set is used.
The present invention also provides a method for generating compressed air by damping a relative motion between an axle and a chassis of a vehicle, wherein the method uses a compressor arrangement which comprises a first element and a second element, wherein the first element can be connected to the axle or the chassis of the vehicle, and the second element can be connected to the other of the chassis or the axle of the vehicle. The compressor arrangement is designed to change an air volume between the first element and the second element in order to generate the compressed air in the case of a relative stroke motion between these elements. The compressor arrangement also has a minimum of the air volume or no air volume between the elements in a position of rest. The method comprises the following steps:
(a) increasing the air volume in the case of a relative motion between the axle and the chassis by entraining the first element in a stroke direction; and
(b) moving the first element counter to the stroke direction, as a result of which a reduction in the air volume is brought about and the compressed air is discharged from the compressor arrangement.
This embodiment variant of the invention in the form of a method also makes it possible for the problem underlying the invention to be solved quickly and efficiently.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.